The present invention relates to novel organometallic complexes comprising cationic heterocyclic carbenes.
It also relates, as means for the preparation of such organometallic complexes, to dicationic heterocyclic precursor compounds.
A further subject-matter of the invention is a process for the preparation of the above organometallic complexes.
Finally, it also comprises the use, as catalysts, of the said organometallic complexes in a number of chemical reactions.
Organometallic complexes comprising heterocyclic carbenes have already been disclosed in the prior art. Thus, Patent EP-A-0,721,953 discloses complexes comprising noncationic heterocyclic carbenes derived from imidazoline or from pyrazoline and a metal from Groups 8, 9 and 10 of the Periodic Classification of the Elements. Patent EP-A-0,798,041 discloses complexes comprising noncationic heterocyclic carbenes derived from various compounds having 5-, 6- or 7-membered rings and comprising one or more nitrogen and/or sulphur atoms and a metal chosen from palladium, rhodium, nickel, ruthenium and cobalt.
Such complexes are very stable compounds which additionally have the advantage of not forming toxic byproducts during their decomposition. However, they exhibit the disadvantage of not being able to be used in an excessively acidic medium and complexes of metals with the 0 degree of oxidation are not soluble in water, which limits the field of their use.
The present invention therefore first of all relates to organometallic complexes comprising heterocyclic carbenes, characterized in that they correspond to the general formula (I)
[(Z+Xxe2x88x92)mMLn]Yxe2x80x83xe2x80x83(I)
in which:
Z+ represents a 1,2,4-triazolium-5-ylidene ion, at least a portion of the atoms of the ring of which are substituted by hydrocarbon-comprising radicals,
L represents a ligand, which can be ionic or neutral,
M represents a metal chosen from the transition elements from Groups 1b, 2b, 3b, 4b, 5b, 6b, 7b and 8 of the Periodic Classification of the Elements as published in xe2x80x9cHandbook of Chemistry and Physics, 51st Editionxe2x80x9d (1970-1971) of The Chemical Rubber Company,
Xxe2x88x92 represents an organic or inorganic anion,
m represents an integer from 1 to 6,
n represents an integer from 0 to 5,
the sum of m and of n is equal to or less than 6,
Y represents an anion or a cation such that the metal complex is electrically neutral.
For convenience, compounds of formula (I) also including the Y counterion are known as organometallic complexes or metal complexes in the present text.
The 1,2,4-triazolium-5-ylidene ions Z+ correspond to the general formula (II): 
in which R1, R2, R3 and R4, which are identical or different, represent:
a linear or branched alkyl radical or a cycloalkyl radical,
an aryl radical,
an alkyl radical which comprises one or more substituents, such as an aryl radical, an alkoxy radical, a halogen atom or a hydrophilic group, for example:
xe2x80x94COOM1, xe2x80x94SO3M1, or xe2x80x94PO3M1, M1 representing an inorganic or organic cationic residue chosen from a proton, cations derived from alkali metals or alkaline earth metals, or ammonium cations xe2x80x94N(R)4, in the formula of which cations the R symbols, which are identical or different, represent a hydrogen atom or an alkyl radical having from 1 to 4 carbon atoms,
xe2x80x94N(R)3Ya, in the formula of which the R symbols, which are identical or different, represent a hydrogen atom or an alkyl radical having from 1 to 12 carbon atoms and Ya represents an inorganic or organic anion,
xe2x80x94OH,
an aryl or aralkyl or cycloalkyl radical which comprises, on the ring, one or more substituents, such as an alkyl radical, an alkoxy radical, a halogen atom or a hydrophilic group, for example:
xe2x80x94COOM1, xe2x80x94SO3M1, or xe2x80x94PO3M1, M1 representing an inorganic or organic cationic residue chosen from a proton, cations derived from alkali metals or alkaline earth metals, or ammonium cations xe2x80x94N(R)4, in the formula of which cations the R symbols, which are identical or different, represent a hydrogen atom or an alkyl radical having from 1 to 12 carbon atoms,
xe2x80x94N(R)3Ya, in the formula of which the R symbols, which are identical or different, represent a hydrogen atom or an alkyl radical having from 1 to 12 carbon atoms and Ya represents an inorganic or organic anion,
xe2x80x94OH,
R3 also represents a hydrogen atom, R1 and/or R4 can also each represent an organic ligand residue bonded to the nitrogen atom of the 1,2,4-triazolium-5-ylidene ion via an alkylene or arylene radical, it being possible for the said ligand residue to be a phosphite residue, a phosphonite residue, a phosphinite residue, a phosphine residue or an amine residue which is tertiary and aliphatic, cyclo-aliphatic, aromatic or heterocyclic and which acts as ligand L to the metal M.
The preceding organic ligand residues can derive, for example, from phenyl or alkyl phosphites, substituted or unsubstituted by substituents as defined above, or from phenyl or alkyl phosphinites, substituted or unsubstituted by substituents as defined above, or from phenyl or alkyl phosphonites, substituted or unsubstituted by substituents as defined above, or from phenylphosphines or alkylphosphines, substituted or unsubstituted by substituents as defined above.
In such a case, the 1,2,4-triazolium-5-ylidene ion substituted by a R1 and/or R4 radical as defined above is a bidentate or tridentate ligand.
L represents an ionic ligand, such as a halide or a cyanide, or a neutral ligand, such as carbon monoxide, an isonitrile, a phosphine, an organic phosphite, a phosphonate or a phosphonite.
M preferably represents a metal chosen from nickel, cobalt, iron, ruthenium, rhodium, palladium, osmium, iridium, platinum, copper, silver, gold, zinc, cadmium or mercury.
These metals can be in their various degrees of oxidation, including the 0 degree of oxidation.
The Xxe2x88x92 anions are organic or inorganic anions, such as, for example, halides, but are preferably chosen from weakly coordinating anions which are defined with respect to the metal M under consideration. They predominantly constitute the counterions of the 1,2,4-triazolium-5-ylidene ions.
Mention may be made, as non-limiting examples of such weakly coordinating anions, of trifluoromethanesulphonate, tetrafluoroborate, hexafluorophosphate, aluminium tetrachloride, aluminium tetrabromide, aluminium tetrafluoride, aluminium tetraiodide, gallium tetrachloride, gallium tetrabromide, gallium tetrafluoride or gallium tetraiodide.
Another subject-matter of the present invention is the use of dicationic heterocyclic compounds as precursors in the preparation of the organometallic complexes of general formula (I). These dicationic heterocyclic compounds correspond to the general formula (III) 
in which
the R1, R2, R3 and R4 symbols have the meanings shown above for the 1,2,4-triazolium-5-ylidene ions of formula (II),
xe2x80x94X31  represents an anion such as those shown for the general formula (I).
The dicationic heterocyclic compounds of general formula (III) can be prepared by reacting a compound of formula XR2, in which X and R2 have the meanings shown above, with a triazole derivative carrying the R1, R3 and R4 substituents. The preparation can also be carried out in several stages, each stage consisting in reacting a triazole derivative with a compound of formula XR1 or XR3 or XR4, depending on the substituent which it is desired to introduce into the formula of the triazole employed, in order to obtain the dicationic heterocyclic compound of formula (III). The reaction conditions can be adapted from the procedure described in the article by T. J. Curphey and K. S. Prasad, Journal of Org. Chem., 1972, 37, 2259.
The organometallic complexes of formula (I) can be prepared by reacting a dicationic heterocyclic compound of general formula (III) with a compound of the metal M in the presence of an inorganic or organic base. Such a base can be the associated anion of the compound of the metal M or can be added independently to the reaction mixture. This reaction can be carried out in liquid medium, generally by adding the compound of the metal M and, if appropriate, the inorganic or organic base to the solution or suspension of the compound (III). Very clearly, the order of introduction of the various reactants can be modified. The reaction can be carried out at room temperature or, preferably, at a temperature of 25xc2x0 C. to 150xc2x0 C., for example. This temperature can conveniently be that of the reflux of the liquid in which the synthesis is carried out. The separation of the complex of formula (I) can be carried out according to the methods commonly used in chemistry, for example by filtration, by centrifuging or by extraction. The complexes of formula (I) and the dicationic heterocyclic compounds of formula (III) are generally characterized by Nuclear Magnetic Resonance (NMR) or by Infrared or by X-ray diffraction.
The organometallic complexes of formula (I) can be used as catalysts in numerous chemical reactions.
The majority of the organometallic complexes of formula (I) as well as the dicationic heterocyclic compounds of formula (III) have little solubility in or are insoluble in the majority of nonpolar or only slightly polar organic solvents, such as alkanes, cycloalkanes, haloalkanes, aromatic hydrocarbons, alkylaromatic hydrocarbons or ethers. On the other hand, they are soluble in polar solvents. Thus, the dicationic compounds are soluble in particular in tetrahydrofuran, dimethyl sulphoxide (DMSO), nitrites (for example, acetonitrile) or water. Thus, the organometallic complexes of the invention are soluble in particular in nitrites (for example, acetonitrile), DMSO or water. These properties make possible easier separation of these various compounds, in particular by liquid/liquid extraction. Furthermore, they make it possible to carry out catalysis in two-phase medium.
Mention may be made, as non-limiting examples of such reactions, of the hydrosilylation of alkenes or of alkynes, in particular in the presence of ruthenium complexes, the hydrosilylation of ketones in the presence of ruthenium or rhodium complexes, the Heck reaction in the presence of palladium complexes, the hydrogenation of olefins, aldehydes, acids, enamides and nitroaromatic compounds in the presence of ruthenium, rhodium, platinum or palladium complexes, the hydroformylation and the hydrocarbonylation of olefins in the presence of rhodium complexes, the hydrocyanation of olefins in the presence of nickel complexes, the synthesis of furan in the presence of ruthenium complexes, the metathesis of olefins in the presence of ruthenium complexes, or the polymerization of acrylates in the presence of nickel complexes.